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Rivet analyses reference

ALEPH_1996_S3196992

Measurement of the quark to photon fragmentation function
Experiment: ALEPH (LEP Run 1)
Inspire ID: 398193
Status: VALIDATED
Authors:
  • Frank Siegert
References: Beams: e+ e-
Beam energies: (45.6, 45.6) GeV
Run details:
  • $e^+e^-\to$ jets with $\pi$ and $\eta$ decays turned off.

Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon production inside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energy $z > 0.7$. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function, $D(z)$, is extracted directly from the measured 2-jet rate.

Source code: ALEPH_1996_S3196992.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/ChargedFinalState.hh"
  5#include "Rivet/Projections/IdentifiedFinalState.hh"
  6#include "Rivet/Projections/FastJets.hh"
  7#include "Rivet/Projections/Thrust.hh"
  8
  9namespace Rivet {
 10
 11
 12  /// ALEPH measurement of quark-to-photon fragmentation function
 13  class ALEPH_1996_S3196992 : public Analysis {
 14  public:
 15
 16    /// Constructor
 17    RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_1996_S3196992);
 18
 19
 20    /// @name Analysis methods
 21    /// @{
 22
 23    void init() {
 24      // Set up projections
 25      FinalState fs;
 26      declare(FastJets(fs, FastJets::DURHAM, 0.7), "DurhamJets");
 27      IdentifiedFinalState ifs; //(Cuts::pT > 0);
 28      ifs.acceptId(PID::PHOTON);
 29      declare(ifs, "Photons");
 30      declare(Thrust(fs), "Thrust");
 31      declare(ChargedFinalState(), "CFS");
 32
 33      // Book histograms
 34      book(_h_z_2jet_001 ,1, 1, 1);
 35      book(_h_z_2jet_006 ,2, 1, 1);
 36      book(_h_z_2jet_01  ,3, 1, 1);
 37      book(_h_z_2jet_033 ,4, 1, 1);
 38      book(_h_z_3jet_001 ,5, 1, 1);
 39      book(_h_z_3jet_006 ,6, 1, 1);
 40      book(_h_z_3jet_01  ,7, 1, 1);
 41      book(_h_z_4jet_001 ,8, 1, 1);
 42    }
 43
 44
 45    /// Perform the per-event analysis
 46    void analyze(const Event& event) {
 47
 48      if (apply<FinalState>(event, "CFS").particles().size() < 2) vetoEvent;
 49
 50      const Particles allphotons = apply<IdentifiedFinalState>(event, "Photons").particles();
 51      Particles photons;
 52      for (const Particle& photon : allphotons)
 53        if (fabs(cos(photon.theta())) < 0.95 && photon.E() > 5.0*GeV)
 54          photons.push_back(photon);
 55      if (photons.size() < 1) vetoEvent;
 56
 57      const Thrust& thrust = apply<Thrust>(event, "Thrust");
 58      if (fabs(cos(thrust.thrustAxis().theta()))>0.95) vetoEvent;
 59
 60      const FastJets& durjet = apply<FastJets>(event, "DurhamJets");
 61
 62      for (const Particle& photon : photons) {
 63
 64        PseudoJets jets_001 = durjet.clusterSeq()->exclusive_jets_ycut(0.01);
 65        for (const fastjet::PseudoJet& jet : jets_001) {
 66          if (particleInJet(photon, jet)) {
 67            double zgamma = photon.E()/jet.E();
 68            if (jets_001.size() == 2) _h_z_2jet_001->fill(zgamma);
 69            else if (jets_001.size() == 3) _h_z_3jet_001->fill(zgamma);
 70            else if (jets_001.size() > 3) _h_z_4jet_001->fill(zgamma);
 71            break;
 72          }
 73        }
 74
 75        PseudoJets jets_006 = durjet.clusterSeq()->exclusive_jets_ycut(0.06);
 76        for (const fastjet::PseudoJet& jet : jets_006) {
 77          if (particleInJet(photon, jet)) {
 78            double zgamma = photon.E()/jet.E();
 79            if (jets_006.size() == 2) _h_z_2jet_006->fill(zgamma);
 80            else if (jets_006.size() == 3) _h_z_3jet_006->fill(zgamma);
 81            break;
 82          }
 83        }
 84
 85        PseudoJets jets_01 = durjet.clusterSeq()->exclusive_jets_ycut(0.1);
 86        for (const fastjet::PseudoJet& jet : jets_01) {
 87          if (particleInJet(photon, jet)) {
 88            double zgamma = photon.E()/jet.E();
 89            if (jets_01.size() == 2) _h_z_2jet_01->fill(zgamma);
 90            else if (jets_01.size() == 3) _h_z_3jet_01->fill(zgamma);
 91            break;
 92          }
 93        }
 94
 95        PseudoJets jets_033 = durjet.clusterSeq()->exclusive_jets_ycut(0.33);
 96        for (const fastjet::PseudoJet& jet : jets_033) {
 97          if (particleInJet(photon, jet)) {
 98            double zgamma = photon.E()/jet.E();
 99            if (jets_033.size() == 2) _h_z_2jet_033->fill(zgamma);
100            break;
101          }
102        }
103
104      }
105    }
106
107
108    bool particleInJet(const Particle& p, const fastjet::PseudoJet& jet) {
109      for (const fastjet::PseudoJet& jetpart : jet.constituents()) {
110        if (fuzzyEquals(jetpart.E(), p.E()) &&
111            fuzzyEquals(jetpart.px(), p.px()) &&
112            fuzzyEquals(jetpart.py(), p.py()) &&
113            fuzzyEquals(jetpart.pz(), p.pz())) {
114          return true;
115        }
116      }
117      return false;
118    }
119
120
121    /// Normalise histograms etc., after the run
122    void finalize() {
123      scale(_h_z_2jet_001, 1000.0/sumOfWeights());
124      scale(_h_z_2jet_006, 1000.0/sumOfWeights());
125      scale(_h_z_2jet_01, 1000.0/sumOfWeights());
126      scale(_h_z_2jet_033, 1000.0/sumOfWeights());
127      scale(_h_z_3jet_001, 1000.0/sumOfWeights());
128      scale(_h_z_3jet_006, 1000.0/sumOfWeights());
129      scale(_h_z_3jet_01, 1000.0/sumOfWeights());
130      scale(_h_z_4jet_001, 1000.0/sumOfWeights());
131    }
132
133    /// @}
134
135
136  private:
137
138    /// @name Histograms
139    /// @{
140    Histo1DPtr _h_z_2jet_001, _h_z_2jet_006, _h_z_2jet_01, _h_z_2jet_033;
141    Histo1DPtr _h_z_3jet_001, _h_z_3jet_006, _h_z_3jet_01;
142    Histo1DPtr _h_z_4jet_001;
143    /// @}
144
145  };
146
147
148
149  RIVET_DECLARE_ALIASED_PLUGIN(ALEPH_1996_S3196992, ALEPH_1996_I398193);
150
151}